In the field of actuator drives, load torque blockers are regularly used to enable an unhindered operation of a machine part in both directions by means of a rotary drive, for example with the help of a motor or a hand-wheel, while blocking, in both directions, reverse-acting torques of the driven part on the drive, without an additional braking system being needed therefor.
Electrical actuator drives for operating elements must be designed such that they can transmit, at low rotational speeds (4-180 RPM), high torques (30-500,000 Nm), wherein the transmitted torques must be highly constant at small angles of rotation.
In the case of known actuator drives, torque transmission between an electric motor and an operating element, such as a valve, is accomplished via a speed-reduction transmission. The speed-reduction transmission is necessary, in order to convert the high RPM of the electric motor into the desired, highly constant, drive RPM for actuating the operating element. Preferably, worm-gear transmissions are used as the speed-reduction transmissions and are so embodied that they exhibit a self-braking characteristic. The advantage, that an accidental and undesired rotation of the drive shaft can be effectively blocked by the intrinsic self-braking, is bought with the disadvantage that total efficiency falls.
DE 10 2004 048 366 B1 discloses a direct drive, or direct actuator, in the case of which the drive shaft is directly and immediately connected with the actuating member, or operating element. Thus, there is no interposed, however fashioned, transmission for converting the motor RPM to the drive RPM for actuating the operating element. The exact positioning of the actuator drive is accomplished via a suitable electric control of the electric motor. The disclosed, direct drive is distinguished, especially, by the fact that an additional braking apparatus can be omitted for the electric motor. The blocking occurs electrically, in that the coils of the coil arrangement are short circuited by the control in the case of a separate actuating of the drive shaft via the actuating wheel. If, now, the actuating wheel is actuated, there is induced in the stator of the electric motor a voltage which acts against the torque exerted by the actuating wheel.
Furthermore, the state of the art discloses special mechanical torque, or load torque, blockers. The torque, or load torque, blocker known from DE 8509971 U works according to the jamming roller, or jamming wedge, principle. In this case, a closed, annular housing contains a fitting, cylindrical, inner element, which is connected, secured against rotation, with the output drive part, thus the part to be driven. The cylindrical, inner element has on its periphery a recess, in which are arranged jamming roller, in each case biased in the outer direction by jamming springs. This block rotation of the cylindrical, inner element relative to the annular, outer housing. Arranged between the two jamming rollers is a ridged-shaped input drive part, which is e.g. part of the hand-wheel. If this input drive part is rotated in one or the other direction of rotation, one of the two jamming rollers is released against the force of the pressure spring and the output drive part can be displaced. In this instance, the second jamming roller is free. Reverse torques from the output drive part are, in contrast, blocked in both directions of rotation.
Rotary drives with torque blockers according to the jamming roller principle are used, for example, for position securement on displacement drives for machine parts. Furthermore, they serve e.g. for securement and hand displacement of gate drives, for hatch and window securement, or for rebound safety in the case of control, or shutoff, valves. The disadvantage of the known torque blocker operating according to the jamming roller, or also jamming wedge, principle is to be seen in the fact that these torque blockers can show a critical blocking behavior. Additionally, they experience a relatively high wear, since, by the repeated jamming and subsequent releasing of the jamming elements, the components coming in contact with one another are exposed to high frictional forces. Due to the loss of dimension or possible deformation of the material, a continuing worsening of the blocking function can be experienced. In the case of a consideration from the point of view of economics, it is evident that torque blockers operating on the basis of the jamming roller principle are unsuitable for application at higher RPMs.
WO 2006/0063874 A1 discloses a torque blocker for an actuator drive for likewise preventing the transmission of reverse-acting torques from an operating element onto the drive part. To this end, arranged in a blocking ring are a wrap spring and a two-part drive shaft, with an entrainment mechanism on the input drive side and a blocking mechanism on the output drive side. The entrainment element is mounted on the input drive shaft of the torque blocker, while, on the output drive shaft of the torque blocker, a blocking piece is secured. The two end regions of the entrainment element lie against the inner sides of the spring ends of the wrap spring.
As soon as the torque blocking drive shaft rotates due to a torque introduction from the input drive side, the entrainment element drives with, in each case, one of its end regions, the wrap spring via the inner sides of the spring ends. The wrap spring is, because of this, released from the blocking ring, whereby a rotation of the output drive shaft is possible. If a reverse-acting torque is introduced via the output drive shaft of the torque blocker, e.g. from the valve, then, depending on direction of rotation, the pertinent end region of the blocking piece is pressed from the outside on one of the spring ends, whereby the wrap spring is pressed under force against the blocking ring, whereby a rotation of the output drive shaft is effectively prevented. Also with this known solution, high RPMs cannot be implemented, so that torque blockers operating according to the wrap-spring principle can be very advantageously applied on the transmission output side, but they are less applicable on the transmission input side.
A torque limiter is available from the firm, Ringspann, under the designation, Durchratsch-Sikumat (Through-Ratcheting Sikumat). A brake cone secured to the output drive shaft is, for purpose of braking/locking, pressed via a pressure spring into a corresponding, fixed, housing part. Between the input drive shaft and the brake cone lie, on both sides, inclined switching surfaces with, as required, balls lying therebetween. If a rotation is initiated via the input drive shaft, the balls roll on the inclined planes and press the brake cone out of its seat in the housing. By the interruption of the frictional contact between the brake cone and the housing, a torque is transmitted via the input drive shaft to the output drive shaft. This known torque limiter is embodied as a mechanical safety system, which, upon reaching a set limiting torque, separates the output drive from the input drive, and so protects against damage or down time. Following removal of the overload, the torque limiter automatically re-engages. A limit switch signals reaching of overload, so that suitable countermeasures can be undertaken.
A disadvantage of this known solution is that the braking action is limited by the spring force of the pressure spring. As soon as the output drive torque becomes greater than the braking torque, which is produced by the spring force of the pressure spring, the torque limiter slips and a safe clamping function is no longer assured. This known solution is, therefore, not usable as a torque blocker.